SUMMARY Environment measurement is an important issue for various applications including household robots. Pulse radars are promising candidates in a near future. Estimating target shapes using waveform data, which we obtain by scanning an omni-directional antenna, is known as one of ill-posed inverse problems. Parametric methods such as Model-fitting method have problems concerning calculation time and stability. We propose a non-parametric algorithm for high-resolution estimation of target

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A Target Shape Estimation Algorithm for Pulse Radar Systems Based on Boundary Scattering Transform

Refractive index of biological specimens is a source of intrinsic contrast that can be explored without any concerns of photobleaching or harmful effects caused by extra contrast agents. In addition, RI contains rich information related to the metabolism of cells at the cellular and subcellular levels. Here, we report a no-moving parts approach that provides three-dimensional refractive index maps of biological samples continuously flowing in a microfluidic channel. Specifically, we use line illumination and off-axis digital holography to record the angular spectra of light scattered from flowing samples at high speed. Applying the scalar diffraction theory, we obtain accurate RI maps of the samples from the measured spectra. Using this method, we demonstrate label-free 3-D imaging of live RKO human colon cancer cells and RPMI8226 multiple myeloma cells, and obtain the volume, dry mass and density of these cells from the measured 3-D refractive index maps. Our results show that the reported method, alone or in combination with the existing flow cytometry techniques, promises as a quantitative tool for stain-free characterization of large number of cells.

Three-Dimensional Holographic Refractive-Index Measurement of Continuously Flowing Cells in a Microfluidic Channel.

The use of ultrasonic transducers for process tomography is in its infancy relative to many other techniques, in particular considering the widespread use of ultrasonic transducers in a variety of non-tomographic sensing applications. This review deals with the background sensing principles of ultrasound transducers employed in tomography, their associated advantages and their difficulties, including the critical time required for data collection, and implications for multiple projection tomography. The theoretical and basic practical implementation of tomography systems using ultrasonic transducers is then considered. Finally a review is included of research investigations into the use of ultrasonic-based process tomography systems.

https://iopscience.iop.org/article/10.1088/0957-0233/7/3/007/pdf

Process tomography using ultrasonic sensors

We present a technique for 3D imaging of live cells in translational motion without need of axial scanning of objective lens. A set of transmitted electric field images of cells at successive points of transverse translation is taken with a focused beam illumination. Based on Hyugens’ principle, angular plane waves are synthesized from E-field images of a focused beam. For a set of synthesized angular plane waves, we apply a filtered back-projection algorithm and obtain 3D maps of refractive index of live cells. This technique, which we refer to as synthetic aperture tomographic phase microscopy, can potentially be combined with flow cytometry or microfluidic devices, and will enable high throughput acquisition of quantitative refractive index data from large numbers of cells.

/pdf/synthetic-aperture-tomographic-phase-microscopy-for-3d-1r0f2ub6o7.pdf

Synthetic aperture tomographic phase microscopy for 3D imaging of live cells in translational motion.

Ultrasonic sensors

A new tomographic imaging technique is presented that requires only two rotational positions of an object. Although ideally the angle between the two rotational positions should be 90°, theory predicts that valid results should be obtainable, albeit with reduced spatial resolution, even when this condition is not satisfied. For each rotational position of the object, the data is collected most efficiently by using arrays on both the transmit and the receive sides; the elements of the transmit array are fired sequentially, and for each such firing the received field is measured over all the elements of the receive array. It is shown thot this measurement strotegy firrs up the Fourier space, from which the object can be recovered by simple Fourier inversion. This imaging strategy was derived from the equations of propagation in an inhomogeneous medium with Born and Rytov approximations. A digital implementation is also presented of the proposed algorithm that requires no interpolations in either the frequency or the space domain, and can be carried out with only 2N FFT's for reconstructing an N X Nimage. Since no interpolations are carried out whatsoever, no computational errors are introduced by the algorithm itself. The total computational complexity of the procedure is of the order of Ow3) as compared to O(Ar4) for a filtered-backpropagation algorithm and O(NZ log N) for procedures based on interpolation in the frequency domain. Some computer simulation results have been included to demonstrate the numerical accuracy of the algorithm.

D. Nahamoo

Papers

Synthetic Aperature Diffraction Tomography and Its Interpolation-Free Computer Implementation

Ultrasonic echo imaging with pseudo-random and pulsed sources: A comparative study